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Toothpaste Supply Duration & Repeat-Purchase Budget

Estimate how long a toothpaste tube lasts and its steady-use purchase cost from usable volume, portion size and household usage.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 91.3125 mL tube, no waste, one user and two daily quarter-milliliter portions lasts 182.625 days, or six average months. At 5 per tube, the annualized cost is 10.

Days of supply = tube volume × (1 − waste share)/(0.25 mL × portions per use × daily uses per person × people)

Worked example

Enter these known values and leave the other values blank.

Volume in one tube
91.3125 mL
Share left unused
0 %
Quarter-milliliter portions per use
1 portions/use
Daily uses per person
2 uses/day/person
People sharing the tube
1
Price of one tube
5 USD /piece
Estimated days or months of supply
6 mos
Average repeat-purchase cost
10 USD / yrs

Assumptions and limitations

  • One modeled portion is 0.25 mL. This is an explicit volume assumption for supply budgeting, not advice about the amount appropriate for a child or adult.
  • Tube volume is positive; waste ranges from zero up to, but excluding, 100 percent. Portion amount, daily frequency and whole user count are positive.
  • Supply duration assumes steady usage without leaks, sharing changes or expiration. Monthly units use 30.4375 days; annual units use 365.25 days.
  • Cost is an average rate of replacement spending. It does not round up to the number of whole tubes purchased within a particular calendar year. Mass printed on a tube must be converted using its actual density before entering a volume.

Common questions

Can I enter a tube labeled in grams?

This model uses volume. Grams measure mass, so a density is needed to convert them to milliliters.

Why is annual cost not a whole number of tubes?

It represents average spending at a steady usage rate. Actual purchases happen in whole tubes at particular dates.

References

Bookify uses an explicit assumed volume of 0.25 milliliters per portion instead of the captured mixed conversion constants. Bookify requires a positive whole number of users and positive daily usage for a finite supply duration. The US fluid ounce uses one 128th of the exact US liquid gallon, replacing the rounded captured reciprocal factor. The US customary cup uses one sixteenth of the exact US liquid gallon, replacing the rounded captured cup volume.

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